class Stack(object):
    def __init__(self,limit = 10):
        self.stack = []
        self.limit = limit
    def is_empty(self): #判断是否为空
        return len(self.stack) == 0
    def push(self,data): #压栈
        if len(self.stack)>=self.limit:
            print("栈溢出")
        else:
            self.stack.append(data)
    def pop(self): #弹出栈顶元素
        if self.stack:
            return self.stack.pop()
        else:
            print("空栈不能被弹出")
    def top(self): #查看栈顶元素
        if self.stack:
            return self.stack[-1]
    def size(self): #长度
        return len(self.stack)


stack = Stack()
print(stack.size())

stack.push(1)
stack.push(2)
stack.push(3)
stack.push(4)
print(stack.size())
print(stack.is_empty())
print(stack.pop())
print(stack.top())